The present invention relates generally to sensing and display apparatus, and more particularly to an apparatus capable of both sensing (inputting) an input signal and displaying (outputting) pixel data, which is able to indicate the incidence of light occurring at any time during a polling cycle, which uses a minimum number of address and data lines per cell for both the input and output functions, and which is configured to allow the circuit to provide gain.
As background to the present invention, present sensing and displaying apparatus, such as interactive arrays, often involve as many as 1 million picture elements ("pixels") or more. Each pixel will generally include an arrangement of circuitry which collectively will be hereinafter referred to as a "cell. " Each cell may serve as an independent sensing element, an independent display or display driving element, or both. Of interest herein is the case where each cell is capable of functioning as both a sensing element and a display driving element.
Each cell will generally include a discrete sensing portion including selected circuitry and a photosensitive element whose current-voltage characteristics change in response to the incidence of light. For a discussion of light sensing cells in general, and a novel light sensing cell in particular, see the cross referenced U.S. Pat. No. 5,083,175. Each cell will also generally include a discrete display portion, usually including a control means such as a thinfilm transistor (TFT) or diode for controlling the state of a pixel of an active display matrix. For a general discussion of active display matrices, and control of individual pixels in such matrices, see Manufacturing Hurdles Challenge Large-LCD Developers, IEEE Spectrum, September 1989, pp. 36-40, which is also incorporated by reference herein. For an example of integration of the sensing and display portions, see U.S. Pat. No. 4,655,552, Apr. 7, 1987, to Togashi et. al., which discloses a light sensing circuit which allows data to be input through a display panel.
A number of disadvantages are presented by known sensing apparatus. These include, for example, the requirements that for some sensing apparatus light must be incident on a cell at the same time that the cell is polled (checked for the results of the incidence of light), the need in other sensing apparatus for three or more separate interconnections to each cell, and the incompatibility of still other apparatus with circuitry capable of providing gain, each as described in detail in the aforementioned copending application of Hack et al.
In addition, the integration of sensing and display portions into a single apparatus presents additional problems. For example, the required number of interconnections, the circuit size, and the circuit complexity, increases, while the yield decreases. Related to this is the need to isolate the sensing portion from the display portion in order to prevent the high voltage applied to the display driving lines from disrupting the sensor circuitry, which limits the extent to which the sensor and display portions may be integrated. Also, due to the differing natures of the components of the sensing and display apparatus, fabrication techniques for the two may differ or be incompatible, requiring hybridization and/or complex fabrication procedures.
These and other problems are addressed by various aspects of the present invention, which is summarized then described in detail below.